Bye weeks have their most detrimental effect on the running back position in fantasy football leagues this week, with Matt Forte, Arian Foster, Ray Rice, Danny Woodhead, Chris Johnson and Trent Richardson all on the sideline.

The result is a waiver wire scramble to fill those positions with viable alternatives. The sudden emergence of Chris Ivory, Mike James and Roy Helu Jr., not to mention the likely return of injured Steven Jackson, is timely, given the need for bodies at the position.

The dearth of options only serves to enhance the value of Knowshon Moreno, Eddie Lacy and other reliable veterans. Those players top PennLive's Week 8 position rankings with prime matchups against struggling opponents.

THREE UP

Knowshon Moreno, DEN, vs. Washington: Moreno is a big-time beneficiary of the Broncos' dynamic passing attack, finding room against defenses that spread out to defend Peyton Manning. He leads the NFL in rushing touchdowns (8) and is on pace for a career-high rushing average (4.4 ypc). Moreno has emerged as a must-start option in fantasy leagues, especially against a Redskins defense that has given up five rushing touchdowns in the last two weeks.

Eddie Lacy, GB, at Minnesota: No defense has given up more fantasy points to opposing running backs than the Vikings, which makes Lacy a candidate for a career day this week. Minnesota has allowed seven rushing touchdowns, tied for sixth-most in the NFL, including four scores in the last three games. Lacy, who's rushed for 300 yards in three games since suffering a concussion, should have ample opportunities to rack up yardage and at least one touchdown.

Marshawn Lynch, SEA, at St. Louis: New year, same story for Lynch, who ranks among the most consistent producers in fantasy football with 578 powerful yards (2nd-most in the NFL) and seven total touchdowns (5th). He faces a Rams defense that ranks 30th against the run and has given up seven rushing scores. It's the same unit that Lynch torched for 218 yards and a touchdown in two meetings last season.

THREE DOWN

Giovani Bernard, CIN, vs. New York Jets: Bernard's usage has been unpredictable in a platoon with BenJarvus Green-Ellis, and he's been held to 10 carries or fewer in five of seven games. He's shown flashes as a receiving threat, but can be neutralized by a Jets defense that leads the NFL in average yards per carry (3.1 ypc). Between the up-and-down workload and the matchup, it's best to temper expectations this week.

C.J. Spiller, BUF, at New Orleans: Spiller (ankle) is listed as questionable for this week, but his absence would be mercy on his fantasy owners. He's the second-best option in the Bills' backfield behind Fred Jackson, who has performed better and gotten a bulk of the goal-line and red-zone work. There's no reason to expect that trend to reverse, especially as Spiller continues to be hobbled by a sore ankle.

Jacquizz Rodgers, ATL, at Arizona: Steven Jackson (thigh) is expected to return for Week 8, which again relegates Rodgers to a part-time role. He's still worth a look as a FLEX option, especially in PPR leagues, but his run of four touchdowns in two weeks is likely over. At least until Jackson gets dinged again.

WAIVER WATCH

Mike James, TB, vs. Carolina: This is not a friendly matchup on paper, which should give pause to those looking to pluck James off waivers. But this matchup should be monitored closely to see exactly what the rookie is made of. James, remember, is making his first start in place of Doug Martin, who is expected to miss significant time with a shoulder injury.

TOP 40 RANKINGS

A look at the top 40 projected running backs for Week 8 with opponents' defensive ranks against the run, rushing touchdowns allowed, total and scoring defense.